1. Field of the Invention
This invention relates to a device for measuring absolute pressure.
2. Prior Art
Known absolute pressure sensors include capacitive transducers which provide a variation in electrical capacitance as a function of pressure. The pressure can act upon the "plates" of the capacitive transducer, the aligned areas of such plates, the type of dielectric material between the capacitive plates, and combinations of these. All of these capacitive transducers have the common characteristic that an electrical signal is detected and provides an indication of the magnitude of the capacitance which, in turn, is an indication of the pressure to be measured.
Another characteristic of such capacitive transducers is the need for a reference atmosphere. Such a reference atmosphere, reference pressure, or vacuum is also a characteristic of various other pressure sensors such as those with a diaphragm. Typically, the reference pressure is established on one side of the diaphragm and the pressure to be measured is on the other side of the diaphragm. Movement of the diaphragm causes a physical indication of the pressure to be measured. Although the use of a reference pressure is prevalent in absolute pressure sensors, it is undesirable because it adds to the cost of the sensor. A cost increase is particularly undesirable when many absolute pressure sensors must be produced. For example, current automobile vehicles with advanced fuel metering systems use two absolute pressure sensors, one to measure ambient pressure and one to measure intake manifold pressure. Increased future usage is anticipated. In addition to the cost of initially establishing the reference pressure, reliably maintaining the pressure sensor reference can be a problem. Any break in the integrity of the container or walls defining the reference atmosphere would cause malfunctioning of the output pressure sensor. Such malfunction can, of course, result in customer dissatisfaction. These are some of the problems this invention overcomes.